This project will attempt to improve our understanding of mechanisms of vocal control by studying brainstem neuronal activity in vocalizing monkeys. The information is important from the standpoint of understanding normal mechanisms of voice and speech as well as neurological disorders affecting voice and speech. Broadly speaking, this project will study how different groups of neurons in the brainstem of macaque monkeys participate in the control of vocalization. This goal will be achieved through four specific studies: (1) Using awake, vocalizing monkeys as subjects, activity of single neurons in the midbrain periaqueductal gray, a structure known for its importance in vocalization, will be recorded simultaneously with neurons in the nucleus retro-ambiguus, a structure to which it is thought the periaqueductal gray neurons project. Analysis will attempt to relate activity of both neuronal groups to vocalization and laryngeal and respiratory muscle activity. (2) Discrete lesions will be made in those areas of the monkey periaqueductal gray found to be important for vocalization. Analysis of changes in acoustical properties of vocalization and muscle activity will be done in order to provide additional information on the role of this structure in vocalization. The findings of this study have important implications for understanding neural-based voice disorders in humans. Several different types of voice disorders ar observed in people, but our understanding of their etiologies is poor. By comparing properties of monkey vocalizations following the lesions with voice disorders in humans, we may gain greater insight into the human disorders. (3) In anesthetized monkeys, changes in subglottal pressure, laryngeal and respiratory muscle activity will be measured during vocalization elicited by stimulation of the periaqueductal gray. These studies will help to interpret the unit-recording data as well as improve our understanding of normal mechanisms of vocalization. (4) A neuronal tracer substance will be injected into the periaqueductal gray and nucleus retro-ambiguus, and after the monkeys have been sacrificed, histological analysis of the brain tissue will reveal anatomical details of the neuronal connections in the brainstem.